Solar powered system with grid backup

Abstract

A system includes a solar power subsystem that receives power from one or more solar power arrays. A storage control subsystem is coupled to the solar power subsystem to charge a battery from the power received by the solar power subsystem. A grid power control subsystem having an AC to DC converter receives power from a power grid and provides DC voltage to the storage control subsystem. A balance of system control system controls the amount of power received from the power grid as a function of a load, battery charge and received power by the solar power subsystem. The solar array and battery may be sized to provide sufficient power under normal operating conditions, with power being drawn from the grid during abnormal operation conditions.

The invention claimed is: 
     
       1. A method comprising:
 receiving power from a solar array; 
 using the received power from the solar array to charge a battery; 
 applying power from the battery to power a load; 
 drawing power from a power grid as a function of the power drawn from the battery to power the load and the power received from the solar array without providing power back to the grid; 
 monitoring a battery drain rate; 
 determining expected power to be received from the solar array; 
 determining if the battery has sufficient power to power the load prior to the solar array providing power to sufficiently power the load and recharge the battery; and 
 drawing power from the grid if sufficient power from the solar array is not expected. 
 
     
     
       2. The method of  claim 1  and further comprising:
 determining a power requirement to power a load in normal operating conditions; and 
 determining sizes for the solar array and the battery to provide sufficient power to the load during normal operating conditions. 
 
     
     
       3. The method of  claim 2  wherein power is drawn from the grid during abnormal operating conditions. 
     
     
       4. The method of  claim 3  wherein abnormal operating conditions are defined as within selected boundary operating conditions. 
     
     
       5. The method of  claim 4  wherein the size of the solar array is no larger than that needed to supply sufficient power to the load within the selected boundary operating conditions. 
     
     
       6. The method of  claim 1  and further comprising:
 monitoring power from the load, wherein the load comprises multiple loads; and 
 reducing power to selected loads as a function of power received from the solar array and available battery power. 
 
     
     
       7. The method of  claim 6  and further comprising turning off selected loads when insufficient power from the battery and solar array is available. 
     
     
       8. The method of  claim 6  wherein power is reduced to selected loads as a function of a predetermined priority for each load. 
     
     
       9. The method of  claim 6  wherein power is reduced as a function of time of day. 
     
     
       10. The method of  claim 1  wherein the battery is charged in accordance with a charge profile for the battery dependent on battery size and chemistry. 
     
     
       11. A method comprising:
 determining total power requirements for multiple loads for operation during normal operating conditions; 
 determining sizes for a solar array and a battery to provide sufficient power to the loads during normal operating conditions; and 
 selecting a controller to control providing power to the loads and charging battery such that power is drawn from a grid connection during operation outside normal operating conditions. 
 
     
     
       12. A system comprising:
 a solar power subsystem that receives power from one or more solar power arrays; 
 a storage control subsystem coupled to the solar power subsystem to charge a battery from the power received by the solar power subsystem; 
 a grid power control subsystem having a AC to DC converter to receive power from a power grid and provide DC voltage to the storage control subsystem; and 
 a balance of system control system to control the amount of power received from the power grid as a function of a load, battery charge and received power by the solar power subsystem. 
 
     
     
       13. The system of  claim 12  wherein the solar power arrays include photovoltaic arrays. 
     
     
       14. The system of  claim 12  wherein the solar power arrays have a size limited to provide sufficient power under normal operating conditions. 
     
     
       15. The system of  claim 14  wherein balance of system control system draws power from the grid during abnormal operating conditions. 
     
     
       16. The system of  claim 15  wherein abnormal operating conditions are defined as within selected boundary operating conditions. 
     
     
       17. The system of  claim 16  wherein the size of the solar arrays is no larger than that needed to supply sufficient power to the load within the selected boundary operating conditions. 
     
     
       18. The system of  claim 12  and further comprising:
 a battery controller to monitor a battery drain rate; 
 wherein the balance of system control system determines expected power to be received from the solar array, determines if the battery has sufficient power to power the loads prior to the solar array providing power to sufficiently power the loads and recharge the battery, and controls the grid power control subsystem to draw power from the grid if sufficient power from the solar array is not expected. 
 
     
     
       19. The system of  claim 12  and further comprising:
 an application control subsystem to monitor power needed by the load, and to reduce power provided to selected loads as a function of power received from the solar array and available battery power. 
 
     
     
       20. The system of  claim 19  wherein the application control subsystem turns off selected loads when insufficient power from the battery and solar array is available. 
     
     
       21. The system of  claim 19  wherein power is reduced to selected loads as a function of a predetermined priority for each load. 
     
     
       22. The system of  claim 19  wherein power is reduced as a function of time of day. 
     
     
       23. The system of  claim 12  wherein the storage control subsystem comprises multiple batteries and wherein each battery is charged in accordance with a charge profile for the battery dependent on battery size and chemistry.